1. Field of the Invention
The present invention relates to a reticle, a reticle inspection method, and a reticle inspection apparatus, and in particular to those preferably used for defect inspection of patterns formed on a reticle.
2. Description of the Related Art
In fabrication process of semiconductor devices such as LSI, patterns (device patterns) are transferred (light exposure) on a semiconductor wafer using a reticle on which the patterns to be transferred are formed. The reticle after being fabricated is inspected for presence or absence of any defects, where detected defects are corrected.
FIGS. 7A and 7B are flow charts showing conventional procedures for the reticle inspection method.
FIG. 7A is a flow chart showing process procedures of a preliminary evaluation for determining defect specifications of the reticle for discriminating defect from non-defect.
First, an evaluation reticle on which a plurality of representative programmed defects (pattern having probable defects) are arranged is fabricated (step S71).
Next, the programmed defects are transferred onto a semiconductor wafer by light exposure of the evaluation reticle using an actual light exposure apparatus (step S72), and transferability of the defects is confirmed by observing to what size of the defects can be transferred onto the semiconductor wafer (step S73). Based on results of the confirmation on the transferability, defect specifications for the reticle are determined (step S74).
FIG. 7B is a flow chart showing procedures of defect inspection of a product reticle on which patterns of an actual product chip are formed.
First, a product reticle as shown in FIG. 8 is fabricated (step S81).
FIG. 8 is a plan view of a conventional reticle 81 on which patterns of a product chip are arranged. As shown in FIG. 8, the reticle 81 has a plurality of device patterns 83-1 to 83-4 formed in an exposure area (wafer transfer area) exposed by an exposure apparatus. The device patterns 83-1 to 83-4 are respectively those related to the product chip, all of which are identical. Outside an exposure area 82 on the reticle 81, alignment patterns 84 used for positional adjustment of the reticle during the light exposure are arranged. Label areas 85 are those for placing the identification numbers or the like of the reticle.
Referring now back to FIG. 7B, an inspection sensitivity is set based on the defect specifications determined by the preliminary evaluation shown in FIG. 7A (step S82).
Next, defect inspection of the reticle is carried out (step S83). The defect inspection includes comparative inspection for comparing a plurality of device patterns on the reticle with each other, and data collation inspection for collating the device patterns on the reticle with their design patterns.
Whether any defect in the pattern was detected or not by the defect inspection is then judged (step S84). If any defect was detected, the defect is then judged whether it is a substantial defect located on the pattern or not, that is, whether the detected defect should necessarily be corrected or not (step S85). On the other hand, if it was judged in step S84 that no defect was detected, the process comes to an end.
If the detected defect was judged in step S85 as being a substantial defect, an information on the defect (positional information, etc.) is entered for future correction (step S86).
If the defect confirmation on the reticle comes to an end, or if there is no need of additional defect confirmation, the process will be terminated, but if not, the process will be returned to step S84 (step S87).
After completion of processing shown in FIG. 7B, next in a reticle correction process, the defect on the reticle is corrected based on the information on the defect entered in step S86.
All of the defects in the pattern on the reticule are thus corrected, and the process advances to the next step.
In some conventional product reticles, a pattern identical to the device pattern of the product chip formed in the exposure area, or a part of the device pattern is formed on the reticle as a collation pattern used for comparison with the device pattern, separately from such device pattern (see Japanese Patent Application Laid-Open No. Sho 63-163464 and Japanese Patent Application Laid-Open No. Hei 1-244304, for example), for use in the above-described comparative inspection (step S83 in FIG. 7B) for detecting any defect. In the defect inspection of the reticle, the presence or absence of the defect is inspected by comparing the device pattern of the product chip, and by confirming the identity therebetween.